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Preventing false negatives in POC pregnancy tests

We have blogged previously (here and here) about false negative results in qualitative point-of-care (POC) hCG devices due to high concentrations of hCGβcf in urine. We have shown that the majority of qualitative POC hCG devices are actually susceptible to false negative results due to saturation of capture antibodies by high concentrations of hCGβcf. These findings have led to an increased interest in urine hCGβcf measurements.

However, only a few research laboratories quantify hCGβcf, so it is difficult for most clinical laboratories to determine which urine samples have high concentrations of this hCG variant.

Previously, we demonstrated that the Roche Cobas hCG+β assay detects hCGβcf but the Abbott Architect Total β-hCG assay does not. Using that information, in a recent study, we examined the correlation between hCGbcf concentrations as measured by LC-MS/MS and the absolute difference between urine hCG measurement using the Roche Cobas and Abbott Architect assays in fourteen urine samples. The correlation between hCGβcf concentration measured by LC-MS/MS and the Roche-Abbott difference was excellent (r=0.97).

This study indicates that the difference in urine hCG concentration when measured by two automated immunoassays (one that recognizes hCGβcf and one that does not) provides a robust estimate of the urine hCGβcf concentration. Using the linear regression equation (Roche-Abbott difference (in IU/L) = (hCGβcf (pmol/L)*0.131+656)), a urine hCGβcf of 280,000 pmol/L translates into an approximate Roche-Abbott difference of 37,336 IU/L.

There are many unanswered questions about hCGβcf, including: How high do hCGβcf concentrations get during pregnancy? Are some women prone to higher hCGβcf concentrations? Are high hCGβcf concentrations associated with certain clinical symptoms or pathological conditions? The ability to estimate the amount of hCGβcf in urine will allow many more laboratories to study the concentrations of this interesting hCG variant.

See more at: http://www.pregnancylab.net/

About The Author

Professor of Pathology & Immunology, and Obstetrics & Gynecology, Washington University School of Medicine

Dr. Gronowski is a Professor of Pathology & Immunology, and Obstetrics & Gynecology at Washington University School of Medicine (St. Louis Missouri). She is Associate Medical Director of the Clinical Chemistry and Serology & Immunology laboratories at Barnes-Jewish Hospital. Dr. Gronowski received her Ph.D. in Endocrinology- Reproductive Physiology from University of Wisconsin, and is a diplomate of the American Board of Clinical Chemistry. Dr. Gronowski is past president of the American Board of Clinical Chemistry and the American Association for Clinical Chemistry. Her research focuses primarily on the laboratory diagnostics of endocrinology and reproductive physiology with a particular emphasis on maternal fetal medicine. She edited the book entitled “Handbook of Clinical Laboratory Testing During Pregnancy”.